Dynamics of wide binary stars: A case study for testing Newtonian dynamics in the low acceleration regime

TL;DR

This study investigates wide binary stars to test Newtonian gravity in low acceleration environments, finding many such systems exist and could serve as natural laboratories for gravity theories, with future data from GAIA promising more insights.

Contribution

It provides the first detailed analysis of wide binary stars' velocities at large separations to test gravity theories in low acceleration regimes.

Findings

Approximately half of the pairs are consistent with being gravitationally bound.

Identified five wide pairs suitable for testing gravity theories.

Supports the potential of wide binaries as natural laboratories for gravity research.

Abstract

Extremely wide binary stars represent ideal systems to probe Newtonian dynamics in the low acceleration regimes (<10e-10 m/s/s) typical of the external regions of galaxies. Here we present a study of 60 alleged wide binary stars with projected separation ranging from 0.004 to 1 pc, probing gravitational accelerations well below the limit were dark matter or modified dynamics theories set in. Radial velocities with accuracy ~100 m/s were obtained for each star, in order to constrain their orbital velocity, that, together with proper motion data, can distinguish bound from unbound systems. It was found that about half of the observed pairs do have velocity in the expected range for bound systems, out to the largest separations probed here. In particular, we identified five pairs with projected separation >0.15 pc that are useful for the proposed test. While it would be premature to draw any conclusion about the validity of Newtonian dynamics at these low accelerations, our main result is that very wide binary stars seem to exist in the harsh environment of the solar neighborhood. This could provide a tool to test Newtonian dynamics versus modified dynamics theories in the low acceleration conditions typical of galaxies. In the near future the GAIA satellite will provide data to increase significantly the number of wide pairs that, with the appropriate follow up spectroscopic observations, will allow the implementation of this experiment with unprecedented accuracy.